What you really mean is "propogation error" and this is a statistical term that refers to the fact that any measurement that we take with some instrument of measure, may be off slightly due to the fact that the measurement device is not EXACT in its measurement. So there is a "propogation or error" associated with any measurement and we need in any scientific experiment to estimate what they error could be.
In another statistical sense, if we take a sample of a given size and say measure its MEAN or AVERAGE, we know that this is only a representation of the Populaltion's Mean from which this sample was taken. So again we have to have some idea of how far off our sample MEAN may be from the true Mean of the Population. This is often referred to as the Estimate of Error. Of course, the larger the sample the less error is possible and if we use the entire Population, then there is no error of our estimate. wmw